Field of the Invention
The invention relates to a sensing device, and more particularly, relates to a magnetic field sensing device capable of improve the Hall Effect.
Description of Related Art
The Hall Effect is a sensing method widely used to detect physical quantity such as the magnetic field. When current horizontally flows through a device placed under action of a vertical magnetic field, a voltage difference is generated at opposite ends of a device on a current direction perpendicular to a magnetic field direction. A magnitude of such voltage difference is proportional to the magnetic field, and this phenomenon is known as the Hall Effect. In the Hall Effect, the voltage difference generated due to the magnetic field is known as the Hall voltage. Other than sensing the magnetic field, the Hall Effect may also be applied in proximity sensors, counters, tachometers, current sensors and so on.
The Hall voltage and the magnetoresistance (MR) are the two aspects of the Hall Effect. When the Hall device is under action of the magnetic field, a current path increases due to shifts under action of the magnetic field, which causes resistance thereof to change with the magnetic field strength, and this is known as the magnetoresistance. A conventional magnetoresistance device forms a structure close to connection in series, so that the magnetoresistance can effectively increase amount of magnetic field variations. In low magnetic field environment, the resistance is small because current is focused to flow through metal pattern due to difference between conductivities of metal and semiconductor. However, in high magnetic field environment, an overall resistance increases because current is under action of the Lorentz force which reduces current in the metal pattern to cause increases of current flowing through the semiconductor region.
Generally, magnetic field sensitivity of the magnetoresistance device is higher than magnetic field sensitivity of the Hall device. However, the magnetoresistance device cannot effectively identify direction of the magnetic field, thus applications thereof are restricted in fields of the proximity sensors, the counters, the tachometers and so on. On the contrary, although the Hall device is capable of correctly detecting direction and magnitude of the magnetic field, a numerical magnitude being sensed is quite limited. As the numerical magnitude becomes smaller with as dimension of the device reduces, devices such as amplification circuit may be additionally disposed for increasing signal strength, and this may lead to problem of signal to noise (SN) ratio because noise is also amplified. In order to satisfy miniaturization of the device while maintaining the magnetic field sensitivity thereof, a decision usually needs to be made between the magnetoresistance device and the Hall device. The Hall device or the magnetoresistance device in the conventional art is composed of semiconductor materials, a performance thereof is depended on a carrier mobility, and the carrier mobility is depended on temperature. Therefore, the Hall device or the magnetoresistance device in the conventional art has high dependence on temperature. Accordingly, it is needed to develop a sensing device which is capable of taking consideration of the both the sensing capability to the magnetic field direction and the high sensitivity to the magnetic field, which is also a sensing device having less dependence on temperature for the magnetic sensing property.